1. Field of the Invention
This invention relates generally to nasal ventilation systems, and more particularly, to a minimally invasive nasal cannula.
2. Description of Related Art
Conventional nasal ventilators generally consist of tubes and other means for delivering therapeutic gases adapted for use with the nasal or oral passage of a patient. Typically, a nasal ventilation system comprises a gas source and a mechanical ventilator such as a continuous positive airway pressure (CPAP) system, bi-level positive airway pressure (BIPAP) system, or intermittent positive pressure breathing (IPPB) system. The gas may be room air, oxygen-enriched air, or a mixture of other gases, e.g., anesthetic gases.
In such conventional nasal ventilators, the gas is transported by a thin flexible main tube made of an inert material. The main tube terminates at an opening which can be inserted into the patient's nostrils. Typically, a pair of smaller nasal insert tubes protrude from the main tube, or the main tube splits at a Y-junction into two smaller tubes. Each smaller nasal insert tube is generally inserted some distance into a nasal cavity to carry gas to the nostril, thereby increasing the fraction of inspired oxygen.
Additionally, conventional nasal tube systems generally do not provide a positive seal between the nasal insert tubes and the nostrils. Thus, some conventional nasal ventilation systems include a mask that fits over the nose that is intended to provide a space of oxygen-enriched air for inhalation into the lungs for respiration. Such systems frequently suffer from air leaking out around the mask, creating an inability to assure ventilation in many patients.
For example, such conventional nasal ventilation systems use head gear and/or straps to bind the mask in place. But in order to minimize the leakage of the air the straps must be sufficiently tight. The mask, headgear, and/or straps thereby exert uncomfortable pressure on the patient's face and/or head, resulting in such masks and headgear tending to be rather constraining and uncomfortable for the patient.
Additionally, many conventional systems tend to be position dependent, whereby if the mask is moved slightly with respect to the facial contour or with respect to the nose, air leakage occurs. With such systems, the mask can become uncomfortable when not in position, thus requiring the patient to remain stationary in order to alleviate the discomfort and to maintain oxygen inspiration. As a result many patients lose interest in using the nasal mask, defeating the purpose of the ventilation system. Thus, nasal ventilation systems typically rely on a seal between the system and the patient to allow the ventilation system to operate properly.
As an alternative to mask-based ventilation systems, it is known to provide a seal against the inside of a patient's nasal cavity using the nasal cannula itself. For example, U.S. Pat. No. 5,533,506 to Wood discloses a nasal insert having a conical shape and a soft membrane covering the tapered end in conjunction with a washer for sealing against the inside of a patient's nostril. U.S. Pat. No. 6,478,026 also to Wood discloses a nasal cannula having annular sleeves made of a soft pliable material for patient comfort, such as a silicone elastomer, to form a gentle but firm seal with the inner wall of one of the patient's nostrils. U.S. Pat. No. 6,848,446 to Nobel discloses nasal inserts of various pre-configured shapes configured to be self-retaining without the use of straps or ear hooks to hold it in place. Similarly, U.S. Pat. No. 4,648,398 to Agdanowski et al. and U.S. Pat. No. 5,105,807 to Kahn et al. both disclose sponge-like nasal inserts for insertion into the nostrils of a patient that are manually compressible with a relatively slow rate of expansion to achieve a seal with patient nostrils.
U.S. Pat. No. 5,113,857 to Dickerman et al. discloses sealant pads in conjunction with a septum clip for sealing a nasal interface to a patient's nasal openings. The Dickerman et al. sealant pads are formed of a soft resilient material, and are partially inserted into the nostril, but appear to seal, at least partially, against the outer surface of the nasal opening. U.S. Pat. No. 4,753,233 to Grimes discloses nasal cannula with integrated converse excurvated tips that allow the cannula to float in the nares of the patient's nose without a pinch fit like the Dickerman et al. device. Inflatable nasal cannula are disclosed in U.S. Pat. No. 4,273,124 to Zimmerman and U.S. Patent Application Publication No. 2003/0094178 to McAuley et al.
Regarding ventilator systems with seals, various valve systems have been devised to allow a patient to inhale therapeutic gas and also exhale from their lungs. In some conventional ventilation systems, the exhalation valve is positioned at the ventilator or in the tubing some distance from the patient. The air that is exhaled by the patient is trapped in a “dead space” between the patient and the valve. Such ventilation systems with exhale valves tend to be bulky and heavy. Additionally, the patient needs to have a tidal volume (breath) that is a little larger than otherwise needed to compensate for the dead space. This larger tidal volume is noticeable by the patient and can be a nuisance while trying to sleep soundly. To solve this dead space problem, the placement of the exhalation valve in the nasal cannula itself has been proposed, see e.g., U.S. Pat. No. 6,478,026 to Wood.
Other types of conventional nasal tube systems include low flow oxygen systems which merely provide oxygen concentration to the patient. These systems typically provide nasal insert tubes that are loosely inserted into the nasal cavities without a mask or seal. Such systems are low pressure systems for providing oxygen enrichment to the ambient air that the patient breathes, i.e., provide elevated oxygen saturation to the patient. However, such low flow oxygen systems are not ventilators, i.e., they do not provide positive pressure for forced ventilation and/or breathing, and could not function as ventilation systems because of the lack of a seal between the cannula interface and the patient, the smaller tubing size, and the low pressure of the system. Because of the lack of a seal in such low flow oxygen systems, the patient can exhale through nasal passages around the length of tube inserted into the nasal cavity.
The nasal insert tubes of such conventional low flow oxygen systems are generally uncomfortable for the patient because of the length of tube inserted into the nasal cavity. Patients are known to intentionally remove the nasal insert tube because of the discomfort. Additionally, such nasal insert tubes are known to become dislodged from within the nasal passages or “nares” because of patient movement during sleep.
Accordingly, there exists a need in the art for a low flow oxygen system nasal interface apparatus that overcomes at least some of the above-mentioned problems with conventional low flow oxygen system nasal cannula. It would be advantageous to have a nasal cannula that is minimally invasive and generally comfortable for the patient to wear. It would be further advantageous to have a nasal cannula that remains comfortably within a patient's nasal passage. It would be further advantageous to have a nasal cannula that also provides a means for exhaling through the nasal passages as well as for delivering oxygen or other therapeutic gases.